Electrostatic printing apparatus

ABSTRACT

ELECTROSTATIC PRINTING APPARATUS IN WHICH THE RECORDING MEDIUM REMAINS AT THE SAME LOCATION DURING THE CHARGING AND EXPOSURE INTERVALS. THE CHARGING ELECTRODE IS PREFERABLY OF NEDDLE SHAPE AND IS LOCATED IN THE DARK AREA OF THE IMAGE PROJECTED ONTO THE RECORDING MEDIUM SO THAT ITS OUTLINE DOES NOT APPEAR IN THIS IMAGE. IN A PREFERRED FORM OF THE SYSTEM, AFTER EXPOSURE, THE RECORDING MEDIUM IS MOVED IN A FIRST DIRECTION TO THE TONER AND DRYING STATIONS AND THEN MOVED IN THE OPPOSITE DIRECTION PAST THE EXPOSURE STATION TO A DELIVERY STATION.

June 27, 1972 M. 1.. LEVENE ETAL ELECTROSTAT I C PRINTING APPARATUS Filed June 12, 1970 5&3 E23 INVENTORS xqtrtz'n LyLevenetand 2 8117 am m0 0. BY W A TTORNE Y United States Patent 672,763 ELECTROSTATIC PRINTING APPARATUS Martin Lewis Levene, Cherry Hill, and Mitsuru Yamamoto, Moorestown, N.J., assignors to RCA Corporatron Filed June 12, 1970, Ser. No. 45,692 Int. Cl. G03g /10 US. Cl. 355-10 4 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION In electrostatic printing apparatus, typically, the photoconductive recording medium is first charged by corona electrodes in darkness. Then, the medium is selectively discharged by being exposed to a projected image of the pattern to be reproduced, light areas becoming discharged. Next, a toner comprising dark charged solid particles in a liquid carrier is applied to the charged areas of the medium to produce a visible image. Finally, these particles are dried in place.

If the charge station and exposing station are separated in space, there is generally no problem in keeping the charged electrode out of the projection path. But, it is often desirable to charge the recording medium and then expose it without first having moved it. This is important, for example, whentime is a factor or when the apparatus must be confined within a very small volume.

The single location charge and expose station creates a problem in that the charging electrodes must be in proximity to the recording medium. The electrodes then interfere with the projection of the image, the source of which is located beyond the electrodes. This results in an undesired shadow of the electrodes appearing on the recording medium and thus the finished document.

When a document must be created in a short time in an apparatus occupying a small volume, a second problem exists, namely that of drying the toner after it has been applied to die recording medium. One solution is to heat the recording medium to dry the liquid carrier which may be Freon. This is not always possible, however. For example, the recording medium may have a glue backing which is activated (placed in a tacky state) by heat and would be prematurely activated if heat was used to dry the toner.

A second solution is to force a stream of air across the toned surface, which both removes excess toner and also dries the toned surface. However, this must be done carefully to avoid a drying procedure which might cause unwanted entrapment of toner particles on uncharged portions of the recording medium.

It is an object of the present invention to provide a rapid, but compact, electrostatic printing apparatus having a single charge and expose station and including also a new and improved means for drying the toner.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic drawing of the apparatus employing the present invention; and

3,672,763 Patented June 27, 1972 FIG. 2 is an example of one type of image which may be reproduced on the recording medium employed in the apparatus of FIG. 1.

SUMMARY OF THE INVENTION An apparatus for electrostatically producing a charge pattern on a photoconductive recording medium includes an electrode for charging the medium and a means for projecting a light image, comprising at least one dark area, onto the medium and electrode where said electrode is substantially located in the dark area so that the image projected onto the medium does not include the outline of the electrode. In a preferred form of the invention, the charged and exposed medium is moved in a first direction past toning and drying stations to create a visible print of the light image and then moved in the opposite direction to a delivery station.

DETAILED DESCRIPTION FIG. 1 shows the present invention employed in an electrostatic printing apparatus for making labels. A web of photoconductive recording medium 12 is supplied from a roll rotatably mounted on hub 14. The hub is rotatably but frictionally attached to a stud 15 (shown in phantom) which is secured to the base plate 10. A cover 16 with a handle 18 is removably attached to the stud to ensure that the web roll will remain in place.

The recording medium 12, as it exits from the roll, passes over a pulley 20, which is rotatably secured to an arm 22. The arm is rotatably attached at its opposite end to a stud 24, which projects from plate 10. A tension spring 26 urges pulley 20 to the right for the purpose of taking up any slack in the Web 12. The web next passes over a guide pulley 30, rotatably attached to the base plate 10, and past a guide pin 32. The web next passes above a drive roller 34 and beneath an idler roller 36, which is spring loaded by tension spring 38 to push the recording medium downward against drive roller 34. The drive roller is coupled by means of belt 39 (shown in phantom) to a suitable drive means 40, such as a bidirectional stepper motor.

Idler roller 36 is attached to an arm 42, which is pivotally mounted on a stud 44 attached to plate 10. A second arm 46 to which spring 38 is attached is also pivotally mounted to stud 44. Arm 46 may be raised upward by means of a handle 48 attached to the arm. This arrangement permits idler roller 36 to be raised away from engagement with the recording medium.

The recording medium, after it leaves roller 34, passes through the various stations which, taken together, cause the finished label to be produced. The description of the various elements comprising the printer will proceed in the physical order of the elements, not the order in which printing occurs. The medium first passes through a drying station 50 and a toner station 52, respectively. A gas, such as air from the blower 56, is applied through tube 54 and the upper and lower plenum 51 and 53 of the air drying station 50 to the web. The air from the lower plenum 53 dries the lower surface of the web in a manner to be described while the air from upper plenum 51 forms an air film which maintains the web spaced 3. small distance from the bottom surface of that plenum.

In the absence of the air film, the web would be forced into frictional engagement with a backing plate which would substitute for the upper plenum. This would impede horizontal movement of the medium 12. Liquid toner 57 in a bellows like container 58 is supplied by means of a tube 60 to a pivotable applicator orifice head 62 located in the toning station 52. A weight 64 provides the necessary pressure to permit the toner to fiow from the bellows container 58 upward to the toning station 52. A second tube 61 connecting the bellows to a valve 63 permits new liquid toner to be added to the bellows from a source of supply (not shown). A valve 66 acts to cut off the flow of toner when it is not desired.

Unlike toners in many commercially available electrostatic copiers, which usually comprise two liquids mixed by the device, toner 57 comes premixed. It is composed of dark charged particles finely dispersed in a Freon carrier, the latter having the desirable properties of drying rapidly and being an insulator.

The head 62 in the toner station has a row of small openings along its upper surface extending in a direction normal to the direction of recording medium movement, through which the toner flows. The head is pivotally attached to stud 73 which extends from plate 10. The head normally rests some distance from the under surface of recording medium 12 as illustrated in FIG. 1. A valve 66 attached to the head and to which tube 60 attaches, acts to control the flow of toner to the head. A solenoid 75 is coupled to an arm 77 which attaches to the valve. When it is desired to apply toner to the paper, solenoid 75 is energized.

As the solenoid draws the upper portion of arm 77 to the left, the counterclockwise pivoting action of the arm about valve 66 causes the valve to open. Continued movement of arm 77 in the counterclockwise direction causes the entire head to pivot about stud 73 until it is in proximity to, but not quite touching, recording medium 12. This arrangement prevents toner from contacting the recording medium when toning is not desired and prevents the flow of any appreciable amount of excess toner. Additionally the upper surface of head 62, which is electrically grounded, acts as a developing electrode the purposes of which are known to practitioners of the art. Any excess toner flows into a container 70, which completey surrounds orifice head 62, through tubing 72 and into a waste container 74.

The recording medium finally passes through a combination charge and expose station 76 and into a delivery station 78. The charge portion of the charge and expose station comprises a single needle-shaped point source electrode 80 for applying the corona charge to the portion of the recording medium located just above the charging electrode, a ground plane plate 82, and a kilovolt power supply 84. A nonconductive mask 86 (shown in cross section) ensures that the charge pattern will be localized to the desired area on the recording medium. The electrode 80 may be of one-piece construction. Alternately, it may comprise a thin wire such as tungsten wire capable of long life in the high voltage and therefore high heat environment in which it is used, surrounded by a metallic tube to provide strength and rigidity. Electrode 80 may be secured in position by means of a nommetallic transparent material such as a block of plastic (not shown).

The image exposure portion of the charge-expose station consists of a light-tight container 90 which houses a light source 92, lenses 94, 96 and 98 and an image source 100 containing the image to be reproduced. Light source 92 may be an incadescent lamp or as in one practical example, a high intensity xenon flash lamp. Lamp 92 is located at the principal focus of a collimating lens 94. The collimated light from lens 94 is projected through the image source 100. Projection lenses 96 and 98 are identical in focal length and diameter. With the image source 100 located at the principal focus of lens 96, an image is formed at unity magnification on the recording medium, which is located at the principal focus of lens 98. Image source 100 may be a transparency, a different one of which is inserted into an opening in the container 90 for each different image to be recorded on the recording medium. Alternatively, an electronically controlled image source such as a liquid crystal element may be used at 100 to provide a source of predetermined images.

FIG. 2 illustrates one of a family of patterns 100, useful as machine readable labels, which the present system is especially adapted to reproduce. In this particularly bulls-eye patterns, the solid black center region is always present. The presence of a black annulus generally speaking represents a binary one and its absence a binary zero. When the pattern is in place in station 76, the needle-shaped electrode and the center of the bulls-eye are aligned so that the needle lies in the shadow created by this central dark area and does not itself appear on the recording medium 12. The horizontal portion 122 of the electrode is very thin and is located outside the primary focus area of the lens system. Therefore its shadow is sufficiently diffuse that it has substantially no effect on the recording medium.

With certain lens systems, it may be desirable to eliminate even the diffuse shadow of the horizontal portion of the electrode. This can be done by embedding the vertical portion of the electrode in a transparent block of material such as glass or plastic and employing a coating of transparent conductor such as Electropane, a product of LOF, Liberty Mirror Division, applied to the upper surface of the transparent block as the lead corresponding to 122.

Since every practical image source has at least one dark area, if this dark area is located on an extended center line of the vertical portion 120 of electrode 80, no electrode shadow will appear on therecording medium. It is of course possible to move either the image source or electrode or electrodes if more than one is used.

Delivery station 78 includes a cutter 110, shown in cross section, to cut off the completed label from the rest of the recording medium Web and a heated plunger 112. Plunger 112 may contain an electrically operated heating element 114 to activate a glue which may be located on the back or upper surface of the recording medium web 12. The adhesive is used where it is desired to secure the label onto a container, such as container 116 located above the electrostatic printing apparatus. When solenoid 118 is activated, it causes plunger 112 to force the completed label against the under surface of container 116.

In operation, let it first be assumed that the recording medium 12 has been threaded into the device with the leading edge located at the right side of the charge-expose station 76, i.e. at cutter 110. Further, toner head 62 and plunger 112 are in the down position and the blower is off. Tension roller 20 is left of the position shown in FIG. 1 so there is a minimum amount of web between the roll and idler roller 30. Then, power supply 84 produces a pulsed output of approximately 10 kilovolts, which is applied to the electrode 80. Approximately twenty such pulses lasting for about milliseconds in duration are applied to the recording medium 12, which is resting against ground plane 82. Mask 86 ensures that only the desired circular area will be charged, assuming the label of FIG. 2 is to be made. Next, light source 92 is illuminated, which projects the image located at 100 onto the recording medium. If a light pattern similar to the shown in FIG. 2 is utilized, there will always be a dark area in the center of the pattern.

The light areas of the pattern projected onto the recording medium cause discharge of corresponding areas on the recording medium. After the recording medium has been exposed, stepping motor 40 operates in a counterclockwise direction to move the charged and exposed portion of recording medium 12 past toner station 52 and into drying station 50. At the same time, tension roller 20 is pulled to the right by spring 26 to take up slack in the medium. Electronics (not shown) activate solenoid 75 to open valve 66 and to position the orifice head 62 into proximity with the under surface of the recording medium. Liquid toner 57 comprises a Freon carrier suspending charged black particles, which are attracted to the charge patern on the paper, and a liquid adhesive 'Which, when dry, serves to fix the black particles to the charged portion of the recording medium. As the toned recording medium passes into the drying station, air emitted at the drying station from energized blower 56 forces excess toner to the right and, when the leading edge of the recording medium reaches the drying station, off the edge of the recording medium into container 70. This is a very useful and efficient way to eliminate excess toner.

If the drying station 50 was located in another position such as, for example, to the right of the charge-expose station, it would not be possible to force excess toner off the leading edge of the recording medium. Instead, it would have to be forced off the side, which is rather difficult to do uniformly or, alternately, toward the rear of the recording medium. The latter method is unsatisfactory as the toner would tend to collect and dry upstream on the recording medium spoiling areas of the medium next to be used.

After the leading edge of the recording medium has moved past the toner station in a left direction, solenoid 75 is deenergized and the solenoid return spring causes valve 66 to close thereby preventing toner from escaping out the top of applicator orifice head 62 and causes the head to retract away from the recording medium 12. When the leading edge of the recording medium reaches an appropriate point in the interior of the drying station, motor 40 reverses, thereby propelling the recording medium in a clockwise or rightward direction. The air blast continues, thereby ensuring that the recording medium will be fully dried. The recording medium is propelled into delivery station 78. Then cutter bar 110 is activated by a solenoid (not shown) to cut off the completed label. While the next label is being made, electricity is supplied to heater element 114 which activates the adhesive backing on the label. The adhesive becomes tacky in about one-half second. Then, solenoid 118 is energized, forcing plunger 112 and the label riding on the plunger into contact with container 116 causing the label to adhere to the bottom surface of the container.

What is claimed is:

1. Apparatus for electrostatically producing a charge pattern on a photoconductive recording medium comprising, in combination:

an electrode for charging said medium while said electrode is stationary relative to said medium;

means for projecting a light image having light and dark areas onto said medium and said electrode for selectively discharging said medium in accordance with the variations in said light intensity, said electrode being substantially located in one of said dark areas,

whereby said image projected onto said medium does not include the outline of said electrode.

2. The combination as set forth in claim 1, wherein said light image comprises concentric dark annuli surrounding a dark circular center portion and wherein said electrode comprises a needle-shaped electrode lying in the direction of projection of said means for projecting said light image and in the path of projection of said dark circular center image.

3. The combination as set forth in claim 1 further including:

means for developing said image comprising means for applying a toner to said medium of the type whose particles adhere to the charged areas in accordance with the amounts of charge present in each area.

4. In apparatus for handling an elongated Web having an end portion terminating at a free end of said web, in combination:

means for applying a charge pattern to said end portion of said web;

means for applying a liquid toner to the surface of said end portion of said web for producing a visible image corresponding to said charge pattern when applied thereto;

means for directing a stream of gas at said surface; and

means for creating relative movement between said lastnamed means and said web in the direction of the length dimension of said web which closes the distance between the origin of said stream and said free end of said web for forcing said liquid off the free end of said web and evaporating any liquid which remains on said surface.

References Cited UNITED STATES PATENTS 3,443,936 5/1969 Menold 250-495 (61) 3,476,935 ll/l969 Metcalfe et al. 25049.5 (61) 3,516,345 6/1970 Meyer --89 SAMUEL S. MATTHEWS, Primary Examiner 'R. P. GREINER, Assistant Examiner U.S. Cl. X.R. 

